Lung cancer is the most frequent cause of cancer death of both males and females in the United States, accounting for one in three cancer deaths.sup.(1). In the last thirty years, cancer-related survival of this disease has improved only minimally. Successful treatment of this disease by surgical resection and drug chemotherapy is strongly dependent on identification of early-stage tumors. A conceptually attractive early detection approach is to establish the presence of a cancer by evaluation of shed bronchial epithelial cells. In the late 1960's Saccomanno et al. proposed the use of sputum cytology to evaluate cytomorphologic changes in the exfoliated bronchial epithelium as a technique to enhance the early detection of lung cancer .sup.(2). However, clinical trials using combination chest X-ray and sputum cytology have not shown any decrease in cancer-related mortality.sup.(3).
In 1988, Tockman et al. reported a sensitive method for early lung cancer detection by immunostaining cells contained within sputum samples with two lung cancer-associated monoclonal antibodies.sup.(4). The basis for this approach was to identify early pre-neoplastic changes in cells shed from bronchial epithelium. The antibodies used in that study were mouse monoclonal IgG's designated 703D4, disclosed in U.S. Pat. No. 4,569,788, and 624H12. In an analysis of the contribution of the individual monoclonal antibodies to early detection of lung cancer, 703D4 alone identified 20 of the 21 detected true positive cases (4; U.S. Ser. No. 08/152,881 which issues to U.S. Pat. No. 5,455,159 on Oct. 3, 1995). 624H12 has been shown to detect an oncofetal antigen which is the Lewis.sup.x -related portion of a cell-surface glycoprotein (Mulshine/Magnani). The antigen for 703D4 was unknown.
703D4 was developed by immunization using a whole tumor cell extract, coupled to keyhole limpet hemocyanin, and selection was based on discrimination amongst subtypes of lung cancer histological subtypes. Preliminary studies showed the 703D4 antibody recognized a protein expressed by most non-small cell lung cancer cells.sup.(5). Immunoprecipitation defined a protein of Mr&gt;31 kDa. Since 703D4 demonstrated the ability to selectively detect changes related to the development of cancer in shed bronchial epithelium from the proximal airways, the antigen recognized by 703D4 was purified in the present invention to determine its identity and explore its relationship to early lung cancer detection. The present invention uses a biochemical approach for identification of the epithelial protein from non-small cell lung tumor cells.
With cigarette smoking the entire human respiratory tract is exposed to potential carcinogens and is at increased risk for cancer development. This phenomenon has been called "field cancerization" (8). A variety of epithelial changes have been observed throughout the respiratory tract of both smokers and lung cancer patients (8,9), which may be part of the "field" effect. Saccomanno et al. (6) have demonstrated that centrally located squamous carcinomas of the lung develop through a series of identifiable stages, namely squamous metaplasia, squamous metaplasia with atypia (mild, moderate, marked), carcinoma in situ, and invasive carcinoma (6). These findings were confirmed by later animal and human studies (7). This cytomorphologic classification is useful in defining preneoplastic changes in the proximal region of the lung cancer "field". However, comparable events preceding the other major lung cancer histologies, especially those arising in the peripheral lung (terminal and respiratory bronchioles, alveolar epithelium) are not well defined.
The expression of an epithelial protein in both neoplastic and non-neoplastic regions of distal human lung was investigated.